The movement of plates that make up the lithosphere of a planet.

Such movements produce fold mountains and other surface features.

A theory that unifies many of the features and characteristics of continental drift and seafloor spreading into a coherent model and has revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history.

A theory that the earth's lithosphere, the crust and upper portion of the mantle, is divided into about twelve large plates and several small ones which float on and travel independently over the asthenosphere (region in the upper mantle of the earth's interior, characterized by low-density, semiplastic, or partially molten rock material chemically similar to the overlying lithosphere).

The theory revolutionized the geological sciences in the 1960's by combining the earlier idea of continental drift and the new concept of seafloor spreading into a coherent whole.

Each plate consists of rigid rock created by upwelling magma at oceanic ridges, where plates diverge. Where two plates converge, a subduction zone forms, in which one plate is forced under another and into the Earth's mantle.

The majority of the earthquakes and volcanoes on the earth's surface occur along the margins of tectonic plates. The interior of a plate moves as a rigid body, with only minor flexing, few earthquakes, and relatively little volcanic activity.